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聚变装置中边界等离子体的磁鞘层特性

Magnetic Sheath Character of Edge Plasma in Fusion Device

作者: 专业:等离子体物理 导师:刘金远 年度:2010 学位:硕士  院校: 大连理工大学

Keywords

plasma, sheath, magnetic field, Bohm criterion, secondary electron

        采用流体模型研究了聚变装置中边界等离子体的磁鞘层结构,考虑了离子磁化和离子热压强的作用,研究了磁场强度、磁场方向、等离子体密度、离子温度等对鞘层特性的影响,得到了离子温度效应下的壁面悬浮电势和等离子体磁鞘层的玻姆判据。本文以氢离子及其同位素离子为例研究了各种参数下等离子体鞘层的特性。当磁场倾斜的角度增大时,壁面电势的绝对值也增大,鞘层厚度先减小后增大。在鞘边净电荷和离子密度出现了振荡,这是因为在强磁场的作用下离子做回旋运动,离子密度在鞘边出现了起伏。角度越大,振荡越剧烈;当磁场大小增加时,鞘层厚度会减小;当离子温度增加时,鞘层厚度会减小;当等离子体的密度增加时,鞘层厚度也会减小,这是与无磁化等离子体鞘层的性质是一致的。密度较低时,在鞘边离子密度和净电荷密度会出现一个峰值;当离子质量越大时,壁面电势的绝对值越大,鞘层厚度也越大。由于聚变装置中边界等离子体的温度为十几到上百电子伏特,电子或离子与器壁相互作用会产生二次电子,因此本文又研究了二次电子发射对等离子体磁鞘层特性的影响。二次电子的发射使得壁面电势的绝对值和鞘层厚度都减小,二次电子发射系数越大,则壁面电势的绝对值和鞘层厚度越小。在考虑二次电子发射时,通过对磁场大小、磁场方向、不同等离子体等情况下对等离子体磁鞘层特性影响的研究,发现这时得到的结果与无二次电子发射时的结果是一致的。通过对二次电子在鞘层内的密度分布研究,发现离子质量越大,鞘层内二次电子的密度越小,这是因为离子质量越大,壁面电势的绝对值越大,电子到达壁面的速度和能量越小,电子与壁面相互作用产生的二次电子越少;离子温度越高,鞘层内二次电子的密度越大,这是因为离子温度越高,壁面电势的绝对值越小,则电子到达壁面的速度和能量越大,因此电子与壁面相互作用产生的二次电子也越多。
    The magnetic sheath structure of edge plasma in fusion device is investigated by using fluid dynamics method. Ion thermal pressure and ion magnetization are considered and the effects of the intensity of magnetic field, magnetic field direction, different plasma density and ion temperature on the character of plasma sheath are researched. And the suspended potential of the wall and the Bohm criterion of plasma magnetized sheath under the ion temperature effect are also deduced.Take H ion and its isotope as an example, we do research on the character of plasma sheath under many parameters. We get that the absolute of wall potential increase when the magnetic field tilt angle increase, and sheath thickness decrease first and then increase. As angle increasing, the density of net charge and ion appear vibration for the ion gyromotion under the strong magnetic field.; When the intensity of magnetic field increases, the sheath thickness decreases.; When ion temperature is higher,the sheath thickness is lower; When the plasma density is higher, the sheath thickness is lower.The result is the same with the character of plasma sheath without magnetization. In lower plasma density, the density of ion and net charge appear peak value at the boundary of plasma sheath; When ion mass is higher, the absolute value of wall potential is higher, and the sheath thickness is higher.Because the temperature of edge plasma in fusion device is more than ten to one hundred electron volt, the interaction between high energy electrons or ions and wall may creates secondary electrons, and the effects of secondary electrons to the character of plasma sheath are also researched. Secondary electrons emission makes that the absolute value of wall potential and sheath thickness decrease. The coefficient of secondary electrons is higher, and the absolute value of wall potential and sheath thickness are lower. On the considering of secondary electrons emission, through researching the effects of the intensity of magnetic field, magnetic field direction, different plasma density and ion temperature on the character of plasma sheath, we find that the results are the same with the condition of no secondary electrons emission.Based on the research of secondary electrons density distribution in the sheath, we find that ion mass is higher and the density distribution of secondary electrons is lower. It’s because that ion mass is higher, absolute of wall potential higher, the velocity and energy of electrons at the wall lower, and the secondary electrons produced by the interaction of electrons and wall are less.; Ion temperature is higher, and the density of secondary electrons is higher. It’s because that ion temperature is higher, absolute of wall potential lower, the velocity and energy of electrons at the wall higher, and the secondary electrons produced by the interaction of electrons and wall are more.
        

聚变装置中边界等离子体的磁鞘层特性

摘要4-5
Abstract5-6
1 绪论9-15
    1.1 等离子体9-10
        1.1.1 等离子体的定义9
        1.1.2 等离子体的发展9-10
        1.1.3 等离子体的分类及研究方法10
    1.2 等离子体鞘层10-11
    1.3 受控核聚变11-13
        1.3.1 核聚变的发展11-12
        1.3.2 聚变装置中边缘等离子体以及等离子体与器壁相互作用12-13
    1.4 等离子体鞘层研究的发展及本文的结构与内容13-15
2 离子磁化的等离子体鞘层特性15-34
    2.1 物理模型15-21
    2.2 数值计算结果与讨论21-33
        2.2.1 磁场方向对鞘层特性的影响21-26
        2.2.2 磁场大小对鞘层特性的影响26-27
        2.2.3 离子温度对鞘层特性的影响27-29
        2.2.4 等离子体密度对鞘层特性的影响29-31
        2.2.5 不同等离子体对鞘层特性的影响31-33
    2.3 本章小结33-34
3 二次电子发射对离子磁化等离子体鞘层的影响34-58
    3.1 物理模型34-39
    3.2 数值计算结果与讨论39-56
        3.2.1 二次电子发射对鞘层特性的影响39-41
        3.2.2 不同等离子体对鞘层特性的影响41-44
        3.2.3 磁场方向对鞘层特性的影响44-48
        3.2.4 磁场大小对鞘层特性的影响48-51
        3.2.5 离子温度对鞘层的影响51-53
        3.2.6 等离子体密度对鞘层的影响53-56
    3.3 本章小结56-58
结论58-60
参考文献60-62
附录A 附录内容名称62-64
攻读硕士学位期间发表学术论文情况64-65
致谢65-67
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